PROJECT ABSTRACT In cancer clinical trials, it is essential to understand and communicate the negative impact of drugs on patient participants in order to balance risks and benefits. Symptom side effects such as nausea and diarrhea are particularly common and impactful on the patient experience. However, historically this information has been reported by clinicians on behalf of their patients rather than by patients themselves ? a process that has been shown to miss up to half of patients' symptoms. Therefore, the National Cancer Institute (NCI) supported development of the Patient-Reported Outcomes version of the Common Terminology Criteria for Adverse Events (PRO-CTCAE), a library of questions to enable systematic patient self-reporting of side effect information. To date, the PRO-CTCAE questions have been developed and tested for validity and feasibility of use in clinical trials ? work that was led by the investigators on this proposal under contracts to the NCI. However, it is not yet established how best to combine PRO-CTCAE information with traditional measures of treatment impact such as clinician-reported adverse events, time on treatment, drug dose levels, performance status, and hospitalizations. The purpose of this proposal is to advance understanding of the role of the PRO- CTCAE in combination with these traditional measures of treatment impact in assessments of drug tolerability. In this proposal, advanced statistical methods will be used to analyze data from numerous clinical trials accessible to the team through the National Clinical Trial Network (cooperative groups) and industry. The specific aims are to: 1) characterize relationships between the PRO-CTCAE and traditional measures of treatment impact and tolerability; 2) test and standardize analytic techniques for the PRO-CTCAE; 3) refine approaches to analyzing missing PRO-CTCAE data; and 4) develop and refine tabular and graphical data visualizations for longitudinal PRO-CTCAE data. To accomplish these aims, an exceptional multidisciplinary team has been assembled including scientific, clinical, and patient investigators with extensive experience in academic and industry clinical research, and longstanding expertise in patient-reported outcomes, adverse events, biostatistics, psychometrics, clinical trial design/analysis, health disparities, and informatics. This team has successfully led multiple prior national research consortia. The team will work collaboratively and flexibly with other investigators and stakeholders through the planned U01 consortium, and will share data, statistical programming code, and ideas freely. This work is intended to inform best practices for tabulating and reporting PRO-CTCAE data, and will enable more systematic and patient-centered evaluations of tolerability in cancer clinical trials.